In order to perform an ion implantation that impurities are implanted into silicon or a silicon thin film during a process in which a thin film transistor (TFT) is formed on a semiconductor substrate or a liquid-crystal glass substrate, an ion implanting apparatus is used. Exemplary types of ions implanted into the substrate include phosphorus (P), boron (B), and the like. In general, the ion implantation is performed in such a manner that raw material gas containing such exemplary types of ions is supplied to an ion source to be thereby plasmatized and a ribbon-shaped ion beam having a rectangular section, which is accelerated after being extracted from the plasma, is irradiated to the substrate.
Since the raw material gas is used by mixing hydrogen with phosphine (PH3), diborane (B2H6) or the like, when the ion beam extracted from the ion source is directly irradiated to the substrate, unnecessary ions such as hydrogen ions are implanted into the substrate as well as P ions (PHx) or B ions (B2HX) necessary to be implanted. In order to remove such unnecessary ions, Patent Documents 1 and 2 disclose a mass-separation ion implanting apparatus in which the ion beam extracted from the ion source is mass-separated to select a desired type of ion and the selected ion is irradiated to the substrate.
Such a mass-separation ion implanting apparatus includes a mass-separation electromagnet through which the ion beam extracted from the ion source passes and a slit to which the ion beam having passed through the electromagnet is irradiated. For instance, as shown in FIG. 1A, the slit disclosed in Patent Document 1 is configured such that a hole 63 is formed through a slit plate 62. As shown in FIG. 1B, the slit disclosed in Patent Document 2 is configured such that a pair of slit plates 64, 64 are opposed to each other on both sides in a thickness direction of the ion beam (a short dimension of a beam section) so that a gap therebetween is adjustable.
When the ion travels in a uniform magnetic field, the ion rotates at a curvature radius in accordance with electric charge and mass thereof. Accordingly, the mass-separation in accordance with types of ions can be performed in such a manner that the slit is disposed on a path where a desired type of ion among the ion beam having passed through the mass-separation electromagnet arrives.
[Patent Document 1] JP-A-H11-339711
[Patent Document 2] JP-A-2005-327713
In many cases, the mass-separation ion implanting apparatus has been used for not a liquid-crystal panel production, but a semiconductor production. Since a height of the ion implanting apparatus for the semiconductor production is 300 mm or so at maximum, a size of the ion beam may be identical with that of the semiconductor if the ion implantation is performed in a bundle without scanning the substrate. However, as a glass substrate for the liquid-crystal panel production to be subjected to an ion implantation, currently, there is known a glass substrate having a size 730 mm×920 mm. In the glass substrate having such a size, assuming that a scanning operation is performed along a long dimension of the substrate, a dimension in a width direction of the ion beam (a long dimension of the beam section) needs to be 800 mm or so. Since magnetic poles of the mass-separation electromagnet for performing the mass-separation are disposed on both sides in a width direction of the ion beam so as to be opposed to each other, a gap between the magnetic poles of the mass-separation electromagnet needs to be 800 mm or more in order to perform the mass-separation of the ion beam having a width of 800 mm or so.
Considering that the gap between the magnetic poles of the electromagnet having been used for the semiconductor production or an accelerator so far is several hundreds of mm or so at maximum, the gap between the magnetic poles of the mass-separation electromagnet for the liquid-crystal panel to be subjected to the ion implantation is very large. When a magnetic field is formed within such a large gap between the magnetic poles, it is very difficult to form a uniform magnetic field throughout the entire area where the ion beam passes. For this reason, when the ion beam passes through the electromagnet having a large gap between the magnetic poles thereof, a problem arises in that a strength or a direction of the magnetic field applied to the ions within the gap between the magnetic poles becomes different in accordance with a position where the ion beam passes due to the non-uniformity of the magnetic field.
When the ion beam having a rectangular section passes through an area where the magnetic field is non-uniform, the output ion beam becomes non-uniform in current density distribution or a shape of the ion beam section tends to vary from the rectangular shape to a crooked shape. For instance, since the magnetic field formed between the magnetic poles is strongly inclined at a position close to the magnetic poles, as shown in FIG. 2, the shape of the beam section tends to be crooked from the rectangular shape to a ⊂-shape. The reason is because a Lorenz force applied to the ion having passed through a strong part of the magnetic field becomes stronger than that of the ion having passed through a weak part of the magnetic field. In addition, the crooked shape of the ion beam is various in accordance with a type, a specification or a magnetic field generating method of the electromagnet to be used, but may be deformed into an inverse ⊂-shape or other shapes as well as the ⊂-shape.
Since the shape of the ion beam becomes crooked in this way, when the ⊂-shaped ion beam passes through the slit in which the hole is formed through the slit plate as shown in FIG. 1A, a problem arises in that a part of the ion beam leaking from the slit is shielded not to pass therethrough and thus current loss occurs.
When a slit gap becomes large in order to reduce the current loss by using the pair of the slit plates of which the gap is adjustable as shown in FIG. 1B (i.e., in order to increase current amount of the ion beam), a problem arises in that mass-separation resolution of the ion deteriorates.
In addition, as a technique for forming uniform magnetic field to remove drawbacks such as non-uniformity of the current density distribution and the crooked shape of the ion beam, a shape of the magnetic poles may be optimized by configuring the magnetic poles of the electromagnet as movable multi-polar magnetic poles. However, since the magnetic pole is generally made from pure steel or low carbon steel and weighs from several hundreds of kg to 1 ton, a problem arises in that manufacture cost increases upon applying an adjustment mechanism to such magnetic poles.